Physiology of vision

Question 1

What are Ciliary bodies?

Answer 1

thickened anterior parts of the choroid, contain circular longitudinal muscle fibres , produce aqueous humour

Question 2

What is the lens?

Answer 2

The adjustable focus, mediated by ciliary bodies

Question 3

What is the iris?

Answer 3

Pigmented and opaque contains constrictors and dilaters

Question 4

What is the vitreous humour?

Answer 4

A gelatinous substance between the lens and retina

Question 5

What is the aqueous humour?

Answer 5

Clear liquid that nourishes the cornea and lens

Question 6

What is accommodation?

Answer 6

the process by which the curvature of the lens is increased in order to focus on a near object

Question 7

What is the principle focal distance?

Answer 7

The distance between the lens and the principle focus

Question 8

Dioptres

Answer 8

Unit of the refractive power of the lens measured in metres

Question 9

What happens when you increase the curvature of the lens?

Answer 9

It brings the focal point forward

Question 10

What happens when the ciliary muscles contract?

Answer 10

Tension is released on the zonulas, therefore causing the lens to become more rounded

Question 11

What does the iris control?

Answer 11

The quantity of light entering the eye

Question 12

What does the vertical slit in a pupil do?

Answer 12

enhances distance judgement in brighter light

Question 13

What is the sclera?

Answer 13

Outer layer of tough connective tissue which merges with the cornea

Question 14

What is the cornea?

Answer 14

Transparent layer at the front, for physical protection, refraction of light and it is highly sensitive

Question 15

What is the choroid?

Answer 15

Vascularised middle layer

Question 16

What is the retina?

Answer 16

innermost layer that contains sensory cells and neurons

Question 17

What are the two types of cell found in the retina?

Answer 17

Rods and Cones

Question 18

Which layer contains the rods and cones in the retina?

Answer 18

The outermost layer

Question 19

Which layer in the retina contains the ganglion cells?

Answer 19

The innermost layer

Question 20

What are the interneuron cell types that the middle layer contains?

Answer 20

Bipolar cells, Horizontal cells and Amacrine cells

Question 21

What is the optic disc?

Answer 21

The point where the optic nerve leaves the eye and blood vessels enter

Question 22

What is the macula lutea?

Answer 22

A yellowish area near the posterior pole. It marks
the location of the fovea centralis

Question 23

What is the fovea centralis?

Answer 23

thin, rod free and cone packed area that contains no blood vessels

Question 24

What is the tapetum lucidum?

Answer 24

A layer that sits behind the retina that helps to reflect more light to the photoreceptors

Question 25

What are saccadic eye movements?

Answer 25

Rapid, taking many screenshots which the brain can then interpret as a stable image

Question 26

What are slow eye movements?

Answer 26

keeping a fixed visual point when the head moves

Question 27

What is the physiological nystagmus?

Answer 27

When image passes extent of eye movement range, a correcting saccade brings the eye back

Question 28

What is the Pathological nystagmus?

Answer 28

when the eye moves and saccades when the head is still indicating a problem with the vestibular system, horizontal indicate peripheral component problem, vertical indicates central problem

Question 29

What is retinal convergence?

Answer 29

When many rods converge on a single ganglion cell

Question 30

What do ganglion cells detect?

Answer 30

a difference in the light in the central and peripheral region rather than the intensity of the light

Question 31

What happens when the light spot is large enough to cover both the central and the periphery?

Answer 31

They signals cancel out

Question 32

What is a particle of radiation called?

Answer 32

a photon

Question 33

What is the inverse of a dioptre?

Answer 33

The principal focal distance

Question 34

What happens when you look at a near object?

Answer 34

The ciliary muscles contract and lens ligaments/ zonulas relax therefore the lens becomes more rounded

Question 35

What happens when you look at a far away object?

Answer 35

The ciliary muscles loosen therefore the zonulas contract flattening the lens

Question 36

What do the circular muscles in the iris do?

Answer 36

Constrict the iris, letting less light in

Question 37

What do the radial muscles in the iris do?

Answer 37

Dilate the iris, letting more light in

Question 38

What kind of muscle is the iris in mammals and birds/reptiles?

Answer 38

Smooth muscle in mammals and striated muscles in birds/reptiles

Question 39

What kind of ganglia cross over at the optic chiasm?

Answer 39

The medial ganglia, lateral ganglia do not cross over

Question 40

What does the geniculocalacrine tract do?

Answer 40

conducts sensory information to the visual cortex of the occipital lobe

Question 41

What are the two types of blood vessels in the fovea centralis and what are their functions?

Answer 41

Retinal vessels - supply the bipolar & ganglion cells * Choroid plexus - supplies the rods & cones

Question 42

What is the macula lutea?

Answer 42

yellowish area at the back of the eye/ near the posterior pole- it marks the location of the fovea centralis

Question 43

What is the function of the crystals of guanine/riboflavin in some cells?

Answer 43

reflects light enhancing vison ## Footnote tapetum lucidum

Question 44

What is the function of some cells containing melanin?

Answer 44

absorbs melanin to improve visual acuity

Question 45

What is the purpose of herbivores having horizontal rectangular pupils?

Answer 45

It shields the eyes from high sunlight whilst maintaining panoramic vision

Question 46

What is the function of carnivores having horixontal pupils?

Answer 46

greater light control and enhanced distanced judgement

Question 47

What part of the eye is more abundant in cones?

Answer 47

The fovea centralis

Question 48

Which ganglia crosses over at the optic chiasm?

Answer 48

The nasal/medial ganglia lateral ganglia does not cross over

Question 49

What is contra-lateral processing?

Answer 49

This means that both sides of the brain process images from both eyes

Question 50

What is the geniculocalacrine tract?

Answer 50

connedcts the geniculocalacrine nucleus to the visual cortex of the occipital lobe

Question 51

What do the ganglion cells form?

Answer 51

The optic nerve

Question 52

What are the two different types of ganglion cells?

Answer 52

* M-type for movement (magnus) * P-type for shape and detail (parvus)

Question 53

What are the two different types of ganglion cells?

Answer 53

* M-type for movement (magnus) * P-type for shape and detail (parvus)

Question 54

How does the light cause hyperpolarisation?

Answer 54

Cgmp continually keeps the channels open so Na/Ca are continuously flowing in Light converts 11-cis-retinal to 11-trans retinal this activates a G protein which converts cGMP to GMP this then closes the channels hyperpolarisation occurs